The present invention relates to an exhaust-gas filter, and, more particularly, a soot-particle exhaust gas filter, comprising a filter element constructed in layers of filter plates configured in wave form transversely to a flow direction of exhaust gas and, in a continuous layer sequence, are arranged alternately to form with one another inlet passages for raw gas and outlet passages for clean gas.
An exhaust-gas filter shown in DE-OS 33 30 020 Al is configured as a right parallelepiped. Its the filter element comprises a plurality of filter plates arranged in layers one on top of the other. The filter plates have a waved or flat structure transversely to the direction of flow of the exhaust gas, wherein a waved layer alternates layer by layer with a flat layer. For conducting the exhaust gas through the passage side walls, the filter passages formed between the filter plates are closed on alternate sides and thereby form raw-gas and clean-gas passages. The exhaust-gas filter described has, however, the disadvantage that, as the running time of the motor vehicle increases, the volume of the filter and the entry area of the filter are reduced by deposition of combustion residues such as, for example, soot particles, oil ash and fuel additives on the filter wall. As a result, the counterpressure to the exhaust gas increases greatly. This results in a reduction in the engine power and an increase in consumption.
An object of the present invention is to provide an exhaust-gas filter such that clogging of the filter owing to deposition of combustion residues on the filter walls over the running time of the motor vehicle is prevented.
The object is achieved according to the present invention by configured the filter such that the inlet passages have a larger cross-section than a cross-section of the outlet passages, the inlet passages and the outlet being formed by a sinusoidal configuration of the filter plates and respective pairs of mutually neighboring filter plates having an identical phase and periodically, but different amplitude and forming a plate group with a layer structure arranged phase-shifted by 180.degree. with respect to neighboring plate groups.
In the present invention, the raw-gas passages are thus provided with a larger cross-section than the clean-gas passages. Because of the enlargement of the wall area of the raw-gas passages, a significantly higher accumulating capacity of the filter results, which at least delays clogging of the filter to a later time. Furthermore, the raw-gas passages covered by the deposits lie closer together, whereby an improved heat transfer between passages carrying the raw gas is achieved and consequently more favorable thermal preconditions for soot burn-off are created. Altogether, due to the increased storage capacity of the filter and the improved thermal conditions for burning off the soot particles over the running time, clogging of the filter is prevented. In addition, the susceptibility of the filter to burning through of the filter walls during soot burn-off is reduced, since the soot filtered out over the running time is distributed over a larger filter surface.
In a constructionally advantageous development of the present invention, the filter plates are sinusoidally waved transversely to the direction of flow of the exhaust gas. Respective pairs of mutually neighboring filter plates have the same phase and the same period but different amplitude and forming a plate group which in the layer structure is arranged phase shifted by 180.degree. with respect to neighboring plate groups. Raw-gas passages of large cross section or clean-gas passages of smaller cross-section are bounded alternately in continuous layer sequence by mutually neighboring filter plates. As a result, the configuration of an exhaust-gas filter having an enlarged filter area for the raw gas with the same external dimensions as in the case of a conventional exhaust-gas filter is made possible.
According to another advantageous embodiment of the present invention, the waving of a filter plate is formed by wave crest groups of the same amplitude which are connected by deep wave troughs and are for their part in each case composed of wave crests connected to one another by flat wave troughs. In this instance, the layer structure of the filter is made up by a continuous reflection of a filter plate at an imaginary plane which forms a tangent to the vertices of the deepest wave troughs of the respective filter plate. Filter passages of various cross-sections are formed between the filter plates. The filter passages of largest cross-section are assigned to the conducting of raw gas. Apart from the constructional advantage of the external dimensions of the filter element remaining the same with regard to conventional exhaust-gas filters, with at the same time an enlargement of the filter area for raw gas, this embodiment of the invention has the technical advantage in terms of production that only one filter plate form is required for the construction of the exhaust-gas filter.